This application is based on and claims priority from Japanese Application No. HEI 3-202604 filed May 2, 1991, the disclosure of which is incorporated herein by reference.
The present invention relates to an objective lens to be used with optical disk systems. More particularly, the present invention relates to an objective lens suitable for performance measurement at wavelengths different from the operating wavelength, as well as a method of measuring the performance of this objective lens.
Measurements for the testing of lens performance are desirably performed in an environment that is either identical or close to the actual environment in which the lens of interest is to be used. Hence, when one is to perform measurements with rays of light being launched into a lens, it is preferred to use a light source that emits light at what will be the operating wavelength after the lens is installed in the system. However, some lenses are adapted to be used at wavelengths outside the visible range. If the performance of such lenses is measured using rays of light at their operating wavelength which is outside the visible range, the efficiency of measurement is undesirably low. In such a case, it would be desirable to perform a measurement using a light source that emits at a wavelength in the visible range which is different from the operating wavelength at which the lens is to be used.
Conventional objective lenses for use with optical disks are intended to be used either at a single wavelength or within the range of wavelength variations of a light source that occur during operation. Thus, if their performance is measured using a light source that emits at a much different wavelength than the operating wavelength, an undesirably large error will occur. If there is a large spherical aberration at the measuring wavelength, increased errors of measurement are liable to occur when aberrations are measured with an interferometer.